REFLECTOR: Fuel Consumption Performance

Scott Derrick scott at tnstaafl.net
Thu Aug 27 21:00:54 CDT 2009


Terry,

Below is my reply of a month ago when you indicated you were leaning to
50 LOP on the first cylinder to peak.  All the rest being richer.  Which
as I stated a month ago is BAD!

Maybe I misunderstood and you are now running ROP?  Leaning until the
first cylinder reaches peak, and then enriching it until it is 50 ROP? 
That would be the old school acceptable  method.  If you decide to read
the articles below, you will read that  GAMI recommends 75 ROP because
50 ROP may be stressful to some engines  at high power settings and low
altitude.

But, since you were running at 10K or above you can run at any mixture
setting and be fine, as far as detonation is concerned because the
engine cannot produce more than 75% power at full throttle.  

I once again recommend the articles below by  John Deacon about how to
safely  operate these big bore aircraft engines.  They are expensive and
easy harm.
 
Scott


**********************************************************

Terry,

running the first cylinder LOP can put some of the richer cylinders right in
the BAD zone. Thats well... bad!  Thats why you always lean to the last
cylinder when running LOP.  Thats also why you lean to the first cylinder
when running ROP, so all the other cylinders are rich of that point.

you said

"I was afraid my coolest cyl could be 150 LOP before the last cly peaked and
that I could burn that exhaust valve."


Thats exactly backwards. Once a cylinder reaches peak EGT and goes on the
LOP side it will run cooler and cooler the leaner you run it. The absoluter
worst mixture is about 25-50 degrees ROP in terms of detonation and the
timing of peak power pulses.  If your coolest cylinder was running at 150
degrees leaner than the last cylinder to reach 75 LOP it would probably not
be firing due to the too lean mixture.
 
How to operate your engine is a complex topic.  Here is a great set of
articles by John Deacon, I consider a must for any recip operator, whether
you run LOP or ROP.

part 1
http://www.avweb.com/news/pelican/182179-1.html
part 2
http://www.avweb.com/news/pelican/182176-1.html
part 3
http://www.avweb.com/news/pelican/182583-1.html
part 4
http://www.avweb.com/news/pelican/183094-1.html


Here's GAMI's lean test,  a great thing for anybody to do, to see how
balanced their injectors are.

http://www.gami.com/gamijectors/leantest.php


Scott



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